Superconducting materials are well known in the art. Niobium based superconductive materials for example, which require extremely low temperatures, have been used for years for superconducting wire used in electromagnets for particle accelerators.
New, relatively high temperature superconducting materials, including, for example, yttrium-barium-copper-oxide (YBC) and bismuth based and thalium based copper oxide materials may be more practical in many applications where the extremely low temperatures required for niobium based superconductors may not be feasible. (YBC and the others are relatively new crystalline materials that superconduct at temperatures near the temperature of liquid nitrogen.) A problem with high temperature crystalline superconducting materials, including YBC, is that to obtain maximum current density, Jc, when the material is below its critical temperature, T.sub.c, i.e. superconducting, the crystalline superconducting material should be grown on a crystalline surface. Moreover, the crystalline structure of both the substrate and the crystalline superconductor should align with respect to each other. Stated alternatively, when the crystalline structure orientation of a crystalline superconductor differs from the crystal orientation of a substrate supporting the superconductor, the superconducting current density will decrease with increasing crystal orientation deviation between the two crystalline structures. This is so for materials that are anisotropic. (Anisotropic superconductive materials are those in which the critical current density, J.sub.c, can change significantly with crystal orientation.)
It is noteworthy that some niobium-based superconductors do not experience a significant decrease in Jc as the crystal orientation of a substrate changes with respect to the crystal orientation of the superconductor because these superconductors are isotropic crystalline materials. (An isotropic superconductor is one in which the critical current density, J.sub.c, does not change significantly with crystal orientation.) Other conductive crystalline materials however that are grown on a crystalline substrate, including even those that are not superconducting, might suffer a decrease in conductivity or current density Jc when the crystal orientation of the substrate differs with respect to the orientation of the material. A substrate that minimizes conductor/substrate crystalline misalignment might improve Jc for crystalline conductors, particularly crystalline superconductors. Since most conductors that carry current have cross-sectional shapes that are either circular or nearly circular, a substrate having a circular cross section that improves alignment between a crystal structure of the conductive material and the substrate would be an improvement over the prior art.
Many practical applications for conductors require or operate better using a conductive material shaped as a rod (resonators in a microwave cavity filter for example). If a crystalline conductive material must be grown on a rod-shaped crystalline substrate, (such a rod being a single crystal) the crystal orientation of the rod material will orient the crystal structure of the conductor at substantially two regions, opposite each other (separated by 180 degrees) on the surface of the rod. The maximum current density per unit area will exist in only those two regions where the single crystal rod orients the crystalline structure of the superconducting material. The surface of a rod fabricated from a single crystal will have a crystal orientation varying around the circumference of the rod.
Since the optimum geometry for a crystalline substrate on which crystalline superconducting materials is grown is a plane, maintaining near perfect alignment between the substrate structure and the conductive material structure becomes very difficult when a circular cross-sectioned conductor is required. An electrical conductor that has a relatively circular, or near circular cross-section, similar to the cross-section of a wire, cable, or pipe but which has an improved substrate crystal orientation enhancing the current density capability of a crystal and superconductor would be an improvement over the prior art.